The Windows edition of the Naval Strike DLC for Battlefield 4 was to have launched today for premium members today alongside the console editions of the military shooter expansion. The Battlefield Blog, however, explains that the PC version's release is being delayed until they work through an issue they've discovered:

On March 25, Battlefield 4 Premium members on consoles will be able to experience the ultimate sea-to-sea warfare in the third expansion pack for Battlefield 4. Battlefield 4 Naval Strike takes the intense and dramatic water-based combat introduced in Battlefield 4 to four all-new maps set in the South China Sea while introducing a new game mode and vehicle.

However, we are delaying the launch of Battlefield 4 Naval Strike on PC. We’ve detected an issue and it needs to be solved. Quality is our number one priority and we will not release Battlefield 4 Naval Strike on PC until we feel it meets the highest quality level possible. Once we have a confirmed date for PC, we’ll be sure to update those players on our official channels. We appreciate your patience and look forward to seeing everyone on the Battlefield.